(1) Field of the Invention
This invention relates to an optical fiber assembly comprising at least two plastic optical fibers, each plastic optical fiber comprising (1) a core of a polymer having a refractive index n.sub.1 and (2) a cladding of a polymer having a refractive index n.sub.2, said plastic optical fibers being arranged substantially in parallel to each other and embedded in (3) in embedding material of a polymer having a refractive index n.sub.3, and also to a process for the preparation of this optical fiber assembly.
(2) Description of the Prior Art
Optical fiber assemblies, such as those composed of at least two optical fibers arranged substantially in parallel to each other and bonded to each other, are increasingly used as light transmitting members for optical communication, high speed data transmission, various process controls, office automation, computers and the like.
One form of an optical fiber assembly, which is formed of a great number of optical fibers gathered and bonded to each other, is disclosed in Japanese Patent Publication No. 27279/64. According to the process disclosed in this patent publication, a rod of a polymer having a high refractive index is melt-drawn to form a core, and the surface of the core is covered with a polymer having a low refractive index to form a core-cladding step index type optical fiber. A number of so-prepared optical fibers are wound on a drum in parallel to one another, and they are bonded together so that the claddings are closely contacted with each other to form an optical fiber bundle. The optical fiber bundle is cut and opened to form an optical fiber sheet. Since the thickness of the cladding of the optical fiber used in this process is very small, i.e., less than about 50 .mu.m, core-to-core bonding is undesirably formed when these optical fibers are bonded together, with the result that the light transmission characteristics of the optical fiber sheet are reduced. If this optical fiber sheet is bent or an external force is applied for processing or handling, the bonded portions of the optical fibers are broken and deformation is caused in the claddings of the optical fibers. A drastic reduction of the light transmission characteristics also results.
As an optical fiber assembly in which the above-mentioned disadvantage is eliminated, Japanese Patent Publication No. 23165/78 proposes an optical fiber assembly formed of core-cladding optical fibers having a non-circular (for example, rectangular or hexagonal) core section. When a bending force or external force is applied to this optical fiber assembly on handling thereof, breakage of the bonded portions of the optical fibers is not caused. However, since the core of each optical fiber has a non-circular section, the light transmission characteristics of this optical fiber assembly are inferior. Therefore, a need continues to exist for an optical fiber assembly wherein breakage of the bonded portions of the optical fibers does not occur when a bending force or external force is applied thereto, and which also possesses excellent light transmission characteristics.